By Gabrielle Tétrault-Farber and Guy Faulconbridge
GENEVA/MOSCOW (Reuters) -Land mines uprooted and dispersed by floodwaters surging downstream from the breached Kakhovka dam in southern Ukraine could pose a grave danger to civilians for decades to come, the Red Cross said on Thursday.
The vast Soviet-era Kakhovka dam, under Russian control, burst in the early hours of Tuesday, unleashing floodwaters across a swathe of the war zone and endangering the lives and welfare of tens of thousands of people.
Both sides in the Ukraine war blame the other for the destruction of the dam, while some Russian-backed officials said that it might have collapsed from within.
The waters have also washed over countless mines sown during the 15-month war and nobody now knows where they are. They could still be in minefields or stuck in river mud and in fields, gardens and roads across a vast area.
"Mines can, depending on their shape and what they're made of, float for kilometers downstream, (and) particularly plastic-bodied mines can float longer," Erik Tollefsen, head of the Weapon Contamination Unit at the International Committee of the Red Cross (ICRC), told Reuters in Geneva.
He said mines laid in the 1940s and under seawater ever since sometimes still functioned, and the danger would not disappear when the flood waters in southern Ukraine eventually receded.
"The risk would worsen when the water recedes because debris will be covering, potentially, the mines. So you can't see them. This is why we are extremely worried about the situation."
The war in Ukraine, the biggest in Europe since World War Two, has left a huge amount of mines and unexploded ordnance across large parts of Ukraine - a risk campaigners have been warning about since Russia sent in troops in February last year.
Besides anti-personnel mines, both sides have used anti-tank mines and artillery shells. The exact number of mines in Ukraine is unclear, said Tollefsen. "We just know the numbers are massive," he said.
Tollefsen said the issue with mines was not necessarily the nominal number but where they were laid - especially in a heavily agricultural country such as Ukraine.
He said territory downstream from the Kakhovka dam - near front lines in the war - contained fields of anti-personnel and anti-vehicle mines laid by parties to the conflict.
Russian-installed authorities who control part of Ukraine's Kherson region warned residents on Thursday to be vigilant for mines being washed downstream by the floodwaters.
"The flow of mines and other dangerous objects is possible," said a statement by the Russian-backed emergency control centre in the Kherson region, one of five in Ukraine that Moscow claims to have annexed.
"As soon as the water subsides, we will immediately begin engineering exploration of the territories. But for now, be as careful as possible."
During a visit on Wednesday to the city of Kherson, which has been heavily affected by the disaster, Ukrainian Deputy Prime Minister Oleksandr Kubrakov similarly warned of the dangers posed by floating mines and also of the spread of infectious bacteria and hazardous chemicals in the flood waters.
(Editing by Gareth Jones and Mark Heinrich)